The present invention relates generally to flow regulation apparatus, and more particularly, to a valve assembly adapted to permit substantially free flow through the valve in a first direction, while preventing flow through the valve in a second, opposite direction. Even more particularly, the present invention relates to valves commonly known as the "duckbill" type.
Duckbill valves are well known and are typically in the form of a resilient flow regulator member mounted in a fluid flow path and which has as its primary operative components a pair of lips arranged in a converging relationship from an inlet end at the base of the lips to an outlet end. At the outlet end of the regulator, the lips are located adjacent to each other so as to define a slit therebetween. The duckbill regulator is often mounted within a housing in a sealed relationship so that flow through the housing must pass through the regulator as well. In a first or forward direction, flow passes into the regulator through the inlet end, moving toward the slit formed at the outlet end. The flow pressure against the resilient lips opens the slit, allowing the flow to pass out of the regulator. When flow enters the duckbill regulator from a second or a reverse direction, the flow contacts the regulator lips at its outlet end, with the flow pressure against the resilient lips holding the slit in a closed position, thereby preventing flow through the valve.
One of the requirements for one-way flow valves is that the valves must offer little resistance to fluid flow in one direction but will completely stop fluid flow in the opposite direction. Many prior art duckbill valves which are designed to firmly bias the valve lips together in order to completely prevent back flow will not fully open at low inlet pressures. Other duckbill valves which offer little resistance in forward flow conditions have a tendency to leak slightly during low back pressure conditions.
Another desirable characteristic of such valves in certain operating conditions is the ability to control the forward flow pressure at which the valve will open without significantly increasing the pressure drop through the valve. Prior art attempts to provide such valves have included providing reinforcing members around the resilient lips of the regulator, however, these prior art valve modifications have typically been accompanied with large pressure drops as the fluid passes through the valve.
Accordingly, a need exists for a valve assembly allowing fluid flow in a first direction and preventing fluid flow in a second, opposite direction in which virtually all leaks in the back flow direction are prevented, and in which means are provided for controlling the pressure at which forward flow may be initiated without restricting the flow path through the valve and creating a higher pressure drop between the inlet and outlet ends of the valve.